AbstractWe present the first all-sky sample of galaxy clusters detected blindly by the Planck satellite through the Sunyaev-Zeldovich (SZ) effect from its six highest frequencies. This Early SZ (ESZ) sample of 189 candidates comprises high signal-to-noise clusters, from 6 to 29. Its high reliability (purity above 95%) is further insured by an extensive validation process based on Planck internal quality assessments and external cross-identification and follow-up observations. Planck provides the first measured SZ signal for about 80% of the 169 ESZ known clusters. Planck further releases 30 new cluster candidates among which 20 are within the ESZ signal-to-noise selection criterion. Eleven of these 20 ESZ candidates are confirmed using XMM-Newton snapshot observations as new clusters, most of them with disturbed morphologies and low luminosities. The ESZ clusters are mostly at moderate redshifts (86% with z below 0.3) and span over a decade in mass, up to the rarest and most massive clusters with masses above 10 × 1014 M☉.